Manual control apparatus



1945- w. E. EDELMAN 2,370,025

MANUAL CONTROL APPARATUS Filed Oct. 14, 1942 attorney Patented Feb. 20, 1945 MANUAL CONTROL APPARATUS Walter E. Edelman, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, 1 Minneapolis, Minn., a corporation of Delaware Application October 14, 1942, Serial No. 461,989

11 Claims. .(Cl. 74-407) The present invention relate to positioning systems in which a member to be positioned is normally operated by a power means, manual operating means being provided for manually and mechanically positioning the member entirely independently of the power means and is an improvement upon the co-pending application of Russell H. Whempner, Serial No. 461,954, filed in the United States Patent Oflice October 14, 1942.

One of the objects of the present invention is the provision of manual operating means for an element normally positioned by a powermeans wherein the arrangement is such that control over the element cannot be lost regardless of the direction of any force which is applied to the element.

Mor specifically it is an object of my invention to provide an arrangement in which the element to be positioned is selectively connected either to a manual operator or a power operator and cannot, under any circumstances, be disconnected from both of the operators at the same time.

Another object of the invention is the provision of manual operating means for an element that is normally positioned by a power means wherein the arrangement is such that after operation of the element is once taken over by the manual means, the manual means remains in control of the element until the power means is in a predetermined position.

Another'object of the invention is the provision of an arrangement for selectively coupling a manual operator or a power operator to a member to be positioned, it being impossible for both the manual means and the power operator to be uncoupled from the member to be positioned at the same time.

Other objects of the present invention include the provision of a manual operator for a member that is normally positioned by a power operator in which the parts are so arranged and cooperate with each other in such manner that at all times, except during the clutching and declutching operations, the clutching or latching mechanism i positively maintained in one or the other of the two positions-which it is possible for it to assume.

Other objects of the invention will become clear upon a reading of the specification and claims and will be found in the single drawing which discloses a preferred form of my invention with the parts somewhat spread out in order to show their -c'ooperation more clearly.

Turning to the single figure of the drawing, the

present invention is shown as applied to a system of temperature control which may conveniently be utilized to control the temperature of the interior of an aircraft cabin. A member to bepositioned is'shown in th form of an arm l0 which may be connected in any of the usual manners to a heat'control valve or the like. Arm It forms an extension of a plate ll having a somewhat semi-circular shape which is journalled upon or concentrically with a shaft l2 for rotation independently thereof. The shaft l2 comprises the final driven shaft of a power operator herein shown as comprising an electrical motor l3 of the split phase type which is connected to the final driven shaft l2 by means of the usual reducing gear train l4. While the parts have here been shown diagrammatically for the sake of clarity, it will be understood that in actual construction the motor [3, gear train l4 and final driven shaft I! are conveniently a unitary structure with which there is associated a base plate or mounting plate l5 shown in dotted lines. The final driven shaft I2 is journalled in the base plate l5 and of course is further provided with suificient other bearing which have here been omitted so that the essential parts of the apparatus may be shown more clearly.

The final driven shaft i2 is normally coupled to the plate H so that the driven arm 10 is normally mechanically connected to the motor l3. To this end, a substantially circular plate or disk It which lies in front of the plate. II is secured to the final driven shaft I 2 by any suitable means such as the key IT. The disk I6 is provided with a portion l8 of reduced radius which joins the larger radius of the main part of the disk l6 so as to form stop portions l9 and 20. These stop portions cooperate with a stop pin 2| carried by base plate l5 whereby the disk i6 is permitted to move only throughout a predetermined arc.

A latch plate 22 is pivoted to the driven plate II by a pin 23. This latch plate 22 lies in front of driven. plate H in the same plane as disk 16 and is provided witha driving latch 24 which is normally engaged in a notch 25 provided in the disk Hi. In this manner, the disk [6 is normally mechanically connected to the driven plate H so that there is a two-way driving connection between these parts. -As a result, the'motor I3 is normally rigidly connected to the driven arm ID.

With the parts thus far described, and when they are in the position and relationship shown, it will be clear that the arm I0 is positioned exactly in accordance with the movement of the motor l3, which range of movement is limited by the stop pin 2| and the cooperating stop portions l9 and 2|) of the disk I6.

The motor l3 may of course be controlled in any desired manner and is herein shown as being controlled by a temperature sensitive resistance bridge 28 through an electronic amplifier 21. The resistance bridge 28 consists of four resist ance arms interconnected in the usual manner. Included in one of these arms is a temperature sensitive resistance 23 of the usual and known type whose resistance increases upon temperature rise. includes fixed resistance 29. The third and fourth arms of the resistance bridge 23 respectively include fixed resistances 3i and 32 as well as variable portions of a follow-up resistance 33. This follow-up resistance 33 is of the usual type and is conveniently secured to the base plate l5. A cooperating contact arm 34 is carried bya piece of insulating material 35 which is in turn connected to the driven arm Hi. The resistance Another arm of the resistance bridge tion, the second winding of the split phase motor I3 is provided with a current having a phase which lags that of the constantly energized winding of the motor with the result that the motor rotates in the opposite direction. Of course, when the bridge is in balance so that the second winding of the motor I3 is deepergized, the motor remains stationary.

With the parts in the position shown, the temperature of the aircraft cabin to which the temperature sensitive resistance 28 responds is at an intermediate value. The bridge is in balance and the motor I3 is inoperative. Under such conditions, the arm II] is intermediate its extreme positions and the follow-up contact arm 34 is engaging the center of the follow-up or balancing resistance 33. The heat control valve 33 and cooperating contact arm 34 comprise the usual follow-up resistance or balancing resistance for maintaining the bridge circuit 28 in balance.

The resistance bridge 26, electronic amplifier 21 and motor |3 preferably are of the type and are interconnected in the manner fully disclosed in the co-pending application of Albert P. Upton, Serial No. 437,561, filed April 3, 1942. The electronic amplifier 21 is provided with a suitable source of alternating current indicated by the wires 36. It is further provided with bridge power supply terminals 31 and 38. Terminal 3'! of the amplifier 21 is connected, through a wire 40, to an input terminal 33 of the bridge circuit which interconnects those arms including the temperature sensitive resistance 28 and the fixed resistance 3|. Similarly, the terminal 38 of the amplifier 21 is connected, through a wire 4|, with a bridge input terminal 42 which forms the junction of those arms of'the bridge which include the fixed resistances 28. and 32. The amplifier 21 is further provided with amplifier input terminals 44 and 45. Terminal 44 is connected, through a wire 46, to bridge output terminal 41 which forms the junction of that arm containing the temperature sensitive resistance 28 and the arm containing the fixed resistance 29. The other terminal 45 is connected to the contact arm 34 by a wire 48. The right-hand end of the balancing resistance 33 is connected to the lower end of the arm containing the fixed resistance 3| by a wire 50. The left-hand end of the balancing resistance 33 is connected to the lower end of the fixed resistance 32, by wire direction, the second winding of the split phase motor |3 is energized with a current having a phase which leads that of the constantly energized winding. This causes rotation of the motor l3 in one direction. On the other hand, when the bridge 26 is unbalanced in the other direcor other apparatus controlled by the driven arm H1 is therefore positioned in such manner as to operate at fifty per cent of its full capacity.

If the temperature within the aircraft cabin should now rise, this will cause an increas in the resistance of temperature sensitive resistance 28. As a result, the bridge 28 will be unbalanced in a predetermined direction. As stated above, this will result in the amplifier 2T supplying current to the second winding of the split phase motor |3 having a phase different than that of the constantly energized winding thereof with the result that motor |3 will begin rotating. This rotation will be in such direction as to move the final driven arm It! in a clockwise direction to reduce the heating effect of the heat control valve or other heat producing apparatus. Also, such clockwise rotation of the driven arm |0 will move contact arm 34 along balancing resistance 33 towards the lefthand end thereof. This inserts more of the balancing resistance 33 in series with fixed resistance 3| tending to rebalance the bridge. When the driven arm I0 has thus moved far enough in a clockwise direction, the bridge circuit 26 will be rebalanced whereupon the second winding of the split phase motor l3 will be deenergized and further movement of the driven arm |0 will cease. If there should be further temperature increase in the cabin of the aircraft. the arm l8 will be moved in a similar manner to a further extent in a clockwise direction and this may continue until the stop portion 20 of the disk 16 engages the stop pin 2|. When such position is reached, the heat producing apparatus will be completely closed down.

If on the other hand, the temperature of the aircraft cabin should fall, the resistance of temperature sensitive resistance 28 will decrease. This will unbalance bridge circuit 28 in the opposite direction with the result that amplifier 21 will now energize the second winding of the split motor i3 with a current having an opposite phase. As a result, the motor l3 rotates in the opposite direction and the final driven arm I0 is moved counter-clockwise. When the final driven arm ID has reached a position corresponding to the new temperature value in the aircraft cabin, the balancing contact arm 34 will have reached such a position on the balancing resistance 33 as to rebalance the bridge circuit 28. Thereupon, the electronic amplifier 21 deenergizes the second winding of the motor l3 and further operation thereof ceases.

In this manner, the final driven arm l0 and the heat control apparatus is positioned in any portion of its full range of movement in accordance with the temperature fluctuations in the aircraft cabin to which'the temperature sensitive resistance responds.

Under some circumstances and particularly with certain applications of the apparatus herein disclosed, it may be not only desirable but in fact necessary to be able to position the driven arm Ill manually entirely independently of the power operating mechanism including the motor l3. To this end, a manual operating arm 55 is provided. The arm 55 is pivoted on a pin 56 that is carried by the plate 51. Plate 51 is in turn pivoted on or journalled concentric with the final driven shaft l2. Interposed between the arm 55 and the plate 51 is a member 58 which is secured to the plate 51. The member 58 is of such thickness, or is provided with bushings or the like so that plate 51 lies in back of plate H whereas manual operating arm 55 lies in front of latch plate 22. A pin 59 which helps to secure the plate 51 and member 58 together extends forwardly into an oblong opening 60 formed in the arm 55 whereby the amount of pivotal movement of the arm 55 about the pivot 56 is limited. Or, looking at it in another manner, the plate 51, member 58, and manual operator 55 are all integrally connected except that the manual operator 55 has a slight amount of movement relative to the plate 51. The manual operator 55 is normally biased, by means to be described hereinafter, so that the upper part of slot 60 engages the pin 59. The complete assembly, as pointed out above, is pivoted on or journalled concentrically with the final driven shaft S2. The arm 55 is further provided with a latch operating portion defined by a slot 6! formed therein which is adapted to cooperate with a pin 62 carried by the latch plate 22. The latch plate 22, in addition to the driving latch portion 24, is further provided with a manual latch portion 63 which is adapted, under proper conditions, to enter a notch 64 provided in the member 58.

Let us assume that with the parts in the position shown, it is desired to take over manual control of the driven arm H). The manual operator 55 is thereupon moved to the left, or counterclockwise. Since the complete assembly comprising plate 51, member 58 and operator 55 are freely pivoted, and since operator 55 is biased to the position shown in respect to plate 51, the

complete assembly pivots in a counter-clockwise direction. Such movement will bring slot 6| in registry with the pin 62 carried by latching plate 22. When pin 62 lies at substantially the right-hand end of slot 6!, manual latching portion 53 will be in registry with notch 54. A short pin 35 carried by plate 51 engages the edge 8| of plate I i when the notch 64 is in registry with the manual latching portion 63. This pin does not extend beyond plate I! and therefore is not in the path of movement of operator 55. Now, further counter-clockwise rotation of the assembly will be resisted since the pin 30 is engaging plate II that carries latch plate 22 which in turn is at present coupled to the driving disk 15. Therefore, further pressure on manual operator 55 overcomes the bias on it and it pivotsabout pin 55 to the extent permitted by slot fill and pin 59. Such movement of manual operator 55 in relation to plate 51 causes the portion 55 to lift pin 62 and therefore latch plate 22. driving latch portion 24 will therefore move out of notch 25 and simultaneously, the manual latch portion 63 will enter notch 54. This uncouples the power operator from driven member and couples the manual operator 55 thereto.

The

The I proportions of the parts are'such that both the driving latch portion 24 and the manual latch portion 63 are unable to be simultaneously disengaged from their respective cooperating notches 25 and 64. In other words, the latch plate 22 is selectively operable to either latch the power operator or the manual operator to the plate I l but the plate I I can never be uncoupled from both of these operators at the same time.

With the latching action just described having been completed, if the manual operator were then moved back in a clockwise direction it would be possible for the surface 66 in cooperation with the pin 62 to immediately move the latch plate 22 back to the position in which it is shown. In order to prevent this, a locking means is provided for maintaining the manual operator 55 latched to the plate ll after this latching action has once been accomplished' This locking means comprises a locking arm 68 pivoted on a pin 69 that is in turn carried by the plate 51. The lower or left-hand portion of the locking arm 68 is provided with an upstanding portion 10 that is biased to move under the surface 1! provided on the arm 55. This bias is accomplished by a spring 12 which has one end bearing against a pin 13 carried by arm 55, is then wrapped around the pivot pin 69 and has its other end bearing against the upstanding portion 10. This spring constantly biases the locking arm 58 towards its locking position. It is likewise this same spring which biases manual operator 55 so that the upper end of slot 60 normally engages pin 59. As a result, when the manual operating arm 55 has pivoted about the pin 59 against this bias and to the extent permitted by theopening 62, the upstanding portion 10 is moved under the surface 1! so as to lock arm 55 in this new position. The parts 55, 58 and 51 are thus locked together with the manual operator latched to plate 1 I so that upon subsequent reverse movement of arm 55 after latching has once occurred no unlatching operation will be possible. Y

With the parts thus latched and locked .together in the manner described, it will be evident that the plate H and therefore the driven arm I0 may now be positioned manually in exact accordance with the movements of the manual operator 55. Furthermore, since there is only one notch 64 in member 58 andsince there is only one latch portion 63 on latch plate 22 thatcan enter notch 64, it is obvious that the manual operator 55 and driven arm I!) can only be connected together in a single predetermined relationship. It, follows that when they are so connected together, the position of manual operator 55 acts to indicate the position of driven arm I0. During such moven'ients,- the circular formation of the disk 15, except such times as the driving latching portion is in registry with the notch 25, will serve as a further means of holding the latching plate 22 in its manual latching position.

In order to disengage the manual operator 55 and reengage the power means, it is necessary to unlock the locking member 68 so as to free the arm 55 for its limited pivotal movement about the pivot 56. It is also necessary to bring the driving latch portion 24 in registry with the notch 25 in the disk [5. Provision is therefore made for driving the disk IE to a predetermined position whenever the manual operator 55 is moved out of its normal stationary inactive position, and provided that the power means is in operative condition. This is accomplished by unbalancing the bridge 28 in a predetermined manner whenever the manual operator 55 is moved out of its normal inactive position. For this purpose, switch arms and 15 respectively provided with contacts TI and 18 are mounted upon the base plate I5. The switch arm 15 is fixed in position but the switch arm 15 is given an inherent bias or stress such that it tends to move its contactv 18 away from the contact 11. However, when the manual operator 55 is in the inactive position shown, these switch blades are held in engagement with each other. This may be simply accomplished by providing the arm 55 with a piece of insulating material 15 which abuts the switch arm 16 and holds its contact 18 in engagement with the cooperating contact 11 whenever the arm 55 is in the inactive position; Upon the initial movement of arm 55 away from its inactive position, the insulating piece 19 will move away from the switch arm 16, whereupon such switch arm is free to move to switch opening position under the influence of its bias or internal stress.

Opening of this switch has the effect of placing infinite resistance in that leg of bridge 26 which contains the fixed resistance 32, such action is the same as if the temperature sensitive resistance increased greatly. As a result, the motor 13 will be operated to drive the disk IS in valve closing direction. Therefore, if the electrical system is in operative condition when the manual operator is moved out of its inactive position, the bridge will be unbalanced in such a direction as to cause driving of the disk H5 in a clockwise direction to its extreme position wherein the stop portion 20 engages the stop pin 2|.

With the disk [5 in this position, the notch therein will be in registry with the driving latch which pin would be engaged by the upper end of the locking arm 58 whenever the manual operator is placed in the inactive position as shown. Such an arrangement is satisfactory but has a possible disadvantage that the parts are unlocked every time the manual operator is returned to its inactive position even though the power means is inoperative and has therefore not returned disk I6 to the extreme position.

This can have no detrimental eifect, however, since under such conditions the notch 25 would not be in registry with the driving latching portion 24 and upon the next subsequent movement of the manual operator 55 in a counter-clockwise direction the locking means would be relocked. However, I prefer in the absence of proper position of disk l6 to prevent this unlocking operation. To this end, I provide a pivoted unlocking arm. 84 which is pivoted on the base plate l5 by a pin 85. This unlocking arm is normally biased to an inactive position against a pin 86 by means of a spring 8'! having one end; secured to the unlocking arm 84 and its other end secured to a pin 88 carried by the base plate IS. The unlocking arm 84 is provided with an extension 89 in-the path of movement of a pin 90 carried by the disk l6. These parts are so proportioned that the pin 90 engages the extension 89 as the disk 16 moves into its extreme clockwise position with the result that when. the disk [8 has reached such extreme position an extension SI of the unlocking arm 84 engages an upstanding portion 92 carried by the right-hand end of the locking arm 68 and moves such arm to its unlocking position. In this manner, an unlocking action can only take place when two conditions occur. One of these conditions is that the disk [6 be driven to its extreme clockwise position. This is taken care of by opening the circuit to the left-hand end of balancing resistance 33 upon initial movement of the manual operator 55 out of its inactive position and provided of course that the electrical system is in operative condition. This could also be accomplished by unbalancing the bridge in the manner disclosed in the application of Russell H. Whempner heretofore referred to. The second of these matters is taken care of by returning the manual operating arm 55 to its inactive position. Under such conditions, the locking arm 68 is unlocked and the driving latching portion 24 is in registry with the notch 25 in the disk 16 so that these parts are recoupled by the camming action ofsurface 66 upon the last portion of the movement of manual operator 55 into its inactive position.

As heretofore explained, the latch plate 22 can never assume a position in which its latching portions 24 and B3 are both disengaged from their cooperating notches 25 and 64. In order to provide relatively quick movement of the latching plate 22 from its unlatching position to its other latching position and vice versa, and in order to tightly hold the latching plate 22 in either of its positions, I preferably provide an over-center spring 93 having one of its ends secured to a pin 94 carried by the latch plate 22, and its other end secured to a pin carried by th plate II. It has been pointed out how the circular surface of the disk I6 is an added means of maintaining the latching plate 22 in its manual latching position by cooperating with the portion 24 at all times except when the portion 24 is in registry with the notch 25. Similarly, the member 58 is provided with an arcuate extension 96 which cooperates with the end of the latching portion 63 to positivel maintain the latching portion 24 in the notch 25 at all times except when the extension 63 is in registry with the notch 64. Although these functions are not absolutely necessary, they do provide extra safety features and further eliminate any possibility of the apparatus functioning improperly.-

To briefly sum up the operation of my invention, with the parts in the positions shown the power means is connected to th driven arm in so that the driven arm I0 is automatically positioned in accordance with the temperature at the temperature sensitive resistance 28. Regardless of the position of the driven arm ID, the power means may be disconnected therefrom and the arm l0 positioned manually. This is accomplished through a single manual operator 55. Movement of the arm 55 causes counter-clockwise rotation of the complete assembly comprising arm 55, member 58 and plate 51. Then, depending upon the position of the driven arm H! at that particular time, which also determines the position at whichpin 30 will engage the edge 8| of plate H, such counter-clockwise motion of this assembly will at some time during its movement cause the notch 54 to register with latching portion 63. Further movement of operator 55 causes it to pivot on plat 51 to unlatch the power tor at the same time.

means and simultaneously latch the manual operator 55 to the driven arm I0. It will therefore be evident that the unclutching and clutching actions are assured of taking place automatically, regardless of the position of the driven arm l0, upon moving the manual operator 55 from its inactive position to its extreme counterclockwise position. After this uncoupling of the power means and coupling of the manual operator has been accomplished, the arm I is then positionable as desired merely by manipulating the manual operator 55. Thereafter, the power means may not be reclutched until such power means is operative so as to be automatically driven to the extreme position described and until the manual operator is returned back to its inactive position.

It should further be noted that under no conditions can the driven arm l0 be uncoupled from both the power operator and the manual opera- Further, since the latch mechanism provides a positive two-way drive under all conditions, it makes no difference whether or not the driven arm I0 is subject to an unbalanced load or the direction of such unbalanced load.

The power operating means of course need not be electrical. Further, the particular manner in which the power means is controlled is immaterial in so far as the broader aspects of my invention are concerned. Many changes and modifications will occur to those skilled in the art and I therefore intend to'be limited only by the scope of the appended claims.

I claim as my invention:

1. In a positioning system, in combination, a member to be positioned, a power operator therefor, a manual operator therefor, coupling means having first and second positions for selectively coupling said operators to said member arranged to prevent disconnection of said member from both of said operators at the same time under all conditions of operation whereby one or the other of said operators is always connected to said member, said coupling means being operable to cause positioning of said member upon movement of one of said operators, and means to snap said coupling means between its first and second positions.

2. In combination, a member to be positioned, a power driven element, a, manual operator, coupling means normally coupling said member to the power driven element but operable to couple said member to the manual operator, means operated by said manual operator for actuating said coupling means to uncouple the power means from said member and couple the manual operator thereto, latch means operable s an incident to said uncoupling and coupling actions to latch said coupling means in the condition wherein said member is coupled to said manual operator, and means operable as an incident to movement of said manual operator to a predetermined position to unlatch said latch means.

3. In combination, a member to be positioned, a power driven element, a manual operator, coupling means normally coupling said member to the power driven element but operable to couple said member to the manual operator, means operated by said manual operator for actuating said coupling means to uncouple the power means from said member and couple the manual operator thereto, latch means operable as an incident to said uncoupling and coupling actions to latch said coupling means in the condition wherein said member is coupled to said manual operator, means operable as an incident to movement of said manual operator in a manner to uncouple said power means for positioning said power means in a predetermined position, and means operable upon movement of said manual operator to a predetermined position when said power means is in its predetermined position for unlatching said latch means.

4. In combination, a power driven shaft, a

' driven element connected thereto, a, member to be positioned journalled concentrically with the shaft, a manual element also journalled concentrically With said shaft, coupling means carried by said member and selectively movable to engage said driven element or said manual element, and means operable by said manual element upon movement thereof to operate said coupling means, the contour of one of said elements being such as to normally hold said coupling means in engagement with the other of said elements.

5. In combination, a member to be positioned, power means normally coupled to said member for operating the same, manual means for operating said member having a normal inactive position, means operable upon movement of said manual means out of said inactive position to uncouple said power means from said member and to couple said manual means thereto, means to lock said coupling means to maintain said manual means coupled to said member, and means operable upon movement of said manual means back to its inactive position to unlock said locking means.

6. In combination, a member to be positioned, power meansnormally coupled to said member for operating the same, manual means for operating said member having a normal inactive position, means operable upon movement of said manual means out of said inactive position to uncouple said power means from said member and to couple said manual means thereto, means to lock said coupling means to maintain said manual means coupled to said member, and means to recouple said power means to said member including means to unlock said locking means.

7. In combination, a member to be positioned, power means normally coupled to said member for operating the same, manual means for operating said member having a normal inactive position, means operable upon movement of said manual means out of said inactive position to uncouple said power means from said member and to couple said manual means thereto, means to lock said coupling means to maintain said manual means coupled to said member, and means to recouple said power means to said member including means to unlock said locking means as an incident to movement of said manual means back to its inactive position.

8. In combination, a member to be positioned, power means normally coupled to said member for operating the same, manual means for operating said member having a normal inactive position, means operable upon movement of said manual means out of said inactive position to uncouple said power means from said member and to couple said manual means thereto, means to lock said coupling means to maintain said manual means coupled to said member, means operable upon movement of said manual means out of its inactive position to move said power means to a predetermined position, and means operative when said power means is in said predetermined position to unlock said locking means and recouple said power means to said element upon movement of said manual means to its inactive position.

9. In combination, a member to be positioned, a power driven element forpositioning said memher, a manual element for positioning said member, and means having first and second positions for selectively coupling one or the other of said elements to said member, said elements having contours cooperating with said coupling means to positively maintain said coupling means in said first or second position after being moved thereto.

10. In combination, a device to be positioned in a plurality of positions and movable throughout a limited range of movement, powermeans for positioning said device in said plurality of positions, manual means for also positioning said device in said plurality of positions, coupling means selectively operable to couple either said power means or said manual means to said device, and means operable as an incident to movement of said manual means to a position corresponding to the then position of said device in its limited range of movement for operating said coupling means to uncouple said device from said power means and couple it to said manual means whereby the position of said manual means will thereafter indicate the position of said device in its range oi movement.

11. In combination, a member to be positioned, a power driven member, a manual operating member, selective coupling means carried by said member to be positioned which when moved in a first direction couples said member to be positioned to said manual member and when moved in a second opposite direction couples said memher to be positioned to said power driven me ber, one or the other of said power driven and manual members always being coupled to s id driven member, and means operable as an in ident to movement of said manual operating member for operating said coupling means in said first direction to couple said manual member to said member to be positioned, said coupling means maintaining the connection between said manual member and said member to be positioned upon initial reverse movement of said manual member whereby upon reverse movement of said manual member the member to be positioned immediately follows such reverse movement of the manual member.

WAL'I'ER E. EDELMAN. 

